This book constitutes the refereed proceedings of the 9th International Workshop on Quality of Service, IWQoS 2001, held in Karlsruhe, Germany, in June 2001. The 24 revised full papers presented together with six short papers and two abstracts of invited contributions were carefully reviewed and selected from a total of close to 150 submissions. The papers are organized in topical sections on provisioning and pricing, systems QoS, routing, TCP related issues, wireless and mobile networking, aggregation and active networks based QoS, scheduling and dropping, and scheduling and admission control.